Digital Video Broadcasting systems have been defined in terms of standards for a variety of broadcasting media, such as cable and direct satellite broadcasting, and for most stages of the broadcasting chain, from contents origination to decoding at the viewer's television set. Such systems are now in the early stages of adoption.
Typically, a DVB system, such as that using cables for signal distribution, broadcasts a plurality of contents channels (also referred to hereunder as channels) and consists of a head-end, the cable distribution system and a decoder (such as in a set-top box) associated with a television receiver at each subscriber location. At the head-end, illustrated by the exemplary block diagram of FIG. 1 (excluding the shaded area), the contents for the various channels are supplied from respective video tape players and from incoming trunk transmission paths, such as terrestrial or satellite links. The contents of each such channel is digitally encoded, if it is not already input in the proper code and the resultant digital signals from a number of channels are routed to, and combined, within a Multiplexer (MUX), into a single digital transmission stream, called Transport Stream (TS), which, after modulating a certain carrier frequency is fed into the cable system. Usually, a plurality of carriers are broadcast over the system, each one carrying one TS that has been produced within a respective MUX from a corresponding group of channels. Each decoder receives the transmission streams and, according to the channel currently selected by the subscriber, demodulates the appropriate carrier, selects from the corresponding TS the signal bits corresponding to that channel and decodes them—to produce an appropriate video signal for inputting into the television receiver, where the signal is displayed as images on the screen, in the usual way. Obviously, the video signal may also be directed to other devices, such as a computer, a video recorder or a local transmission system.
According to current DVB standards, as published, for example, in ETSI ETR 154, the encoding of each channel is according to MPEG-2 standards, which are well known in the art. Usually each video channel is encoded into a constant stream of between 2 and 6 megabits per second (Mb/s)—depending on the quality assigned to the particular channel. It may thus be said that each channel has a transmission rate capacity of 2–6 Mb/s. Each combined TS (modulating one carrier) has a rate of approximately 38 Mb/s. It thus carries between six and nineteen channels. With, say, 40 carriers, which is typical for a cable system, the total number of channels possible is thus between 240 high-quality channels and over 700 lower-quality channels.
In spite of this seemingly large number of channels available in a system, it is likely that they may not be enough for the needs of broadcasters and subscribers, so that there may be a high value attached to each available channel. Much of the source material intended for such channels has the characteristics of a full video signal, that is—it represents complex images with relatively large amount of motion, such as regular movies, advertisement video and other camera-captured moving scenes. Such material is considered to have “rich” information contents and therefore requires the allocated channel bit rate (e.g. 2–6 Mb/s). On the other hand, there is a large class of video source material that is relatively “lean” in information contents. This class mainly includes “informational” type of programs, such as government—and civic announcements, train schedules, weather forecasts, news and simple advertisements—all of which is characterized by being usually presentable in terms of text, simple graphics and occasional small insets of video clips; the text and graphics may include some animation, which involves simple motion. Clearly, such material, when digitally encoded, e.g. according to any MPEG standard, requires a much lower rate than the minimum of 2 Mb/s of the standard channel in a DVB system. Thus, allocating a complete standard channel to each source of such program material, within a DVB system, is wasteful of system resources and may be uneconomical; that is, the charges levied for each channel by the system operator may be too high for the utility value of broadcasting such sources.
While it is conceivable that the standards of DVB systems may be extended to accommodate channels of ever lower rates, so as to efficiently accommodate “lean” sources of this type, such a course may be rather impractical, because it would greatly increase the complexity of the head-end equipment—especially of the multiplexer—thus greatly increasing its cost, which is high even under present standards (typically about $200,000). Moreover, as will be shown in the discussion of the present invention, such informational video material may be compressed to even lower average bit rates than any predefined rate within such extended-standards DVB systems, so that the efficiency achievable with such an extended-standards system may not be optimal.
There is thus a need, and it would be highly desirable, to have a method, and preferably also an apparatus, for efficiently and economically encoding informational video material and broadcasting it within a currently standard DVB system. The role of such apparatus in a head-end of a DVB system is shown, for example, schematically (marked by a shaded area) in FIG. 1. Here it is seen to be connected so that it receives program materials from various sources over a digital network (which may include the Internet) and to feed a corresponding transport stream, which carries the various materials, as a single channel into the router of the head-end.
It is, moreover, highly desirable that as many programs as possible be thus encodable into a single channel without exceeding its data transmission capacity and without introducing noticeable distortions or other deleterious effects in the received images.
It is, furthermore, highly desirable that the programs from the various sources be individually selectable by the user and that his set-top box be able to decode them as it would any conventional program material, without the need for special modification of the box. In other words, it is desirable that the various programs be treated by external agents as proper channels; in the present context they will be referred to as Micro-channels, or Virtual information channels (VIC). Accordingly, the desired equipment will be referred to as VIC Server.